The invention is concerned with the field of turbomachines and relates to a device for injecting a mixture of air and fuel into a combustion chamber of a turbomachine.
It relates more specifically to an injection device provided with a novel sliding bushing and with a novel annular cup for retaining the sliding bushing, making it possible to improve the air feed of the injection device.
Throughout the remainder of the description, the terms “upstream” or “downstream” will be used to denote the positions of the structural elements with respect to one another in the axial direction, taking the gas flow direction as reference. Likewise, the terms “internal” or “radially internal” and “external” or “radially external” will be used to denote the positions of the structural elements with respect to one another in the radial direction, taking the axis of rotation of the turbomachine or the axis of symmetry of the structure in question as reference.
A turbomachine comprises one or more compressors delivering pressurized air to a combustion chamber in which the air is mixed with fuel and ignited so as to generate hot combustion gases. These gases flow in the downstream direction of the chamber toward one or more turbines which convert the energy thus received in order to rotate the compressor or compressors and provide the necessary work, for example, to power an aircraft.
Typically, a combustion chamber used in aeronautics comprises an internal wall and an external wall interconnected at their upstream end by a chamber end wall. The chamber end wall has, spaced circumferentially, a plurality of openings each accommodating an injection device at the center of which an injector is positioned, the assembly allowing the mixture of air and fuel to be fed into the chamber.
The combustion chamber is supplied by liquid fuel mixed with air from a compressor. The liquid fuel is fed right to the chamber by the injectors in which it is vaporized into fine droplets. This vaporization is initiated in the region of the injector by means of nozzles and is continued particularly in the region of the venturi and the bowl by the effect of pressurized air from a compressor. This pressurized air passes, on the one hand, through the radial swirlers of the injection device so as to cause the fuel sprayed by the injector to rotate, and, on the other hand, through orifices formed in various parts of the injection device, such as the bowl.
As illustrated particularly in document FR 2 753 779, an injection device has a symmetry of revolution and comprises, arranged from upstream to downstream, a sliding bushing connected by an annular cup to radial swirlers. The radial swirlers comprise a venturi and are connected by their downstream end to a bowl with a divergent conical wall. The bowl is itself connected to the chamber end wall via a deflector. According to the prior art, the sliding bushing includes, arranged from upstream to downstream, an upstream wall of convergent conical shape extended by a cylindrical wall, which terminates downstream in an annular flange extending radially outward.
Owing to the convergent conical shape of its upstream part, the sliding bushing constitutes an obstacle that the air coming from the compressor must negotiate. Likewise, since the outside diameter of the annular cup, which serves as radial guide for the sliding bushing, is large, the annular cup itself constitutes an obstacle to be negotiated. This is the origin of air recirculation and substantial pressure drops deleterious to the air feed of the injection device. The spraying quality is therefore degraded, resulting in a larger droplet size, and a coke deposit may appear on the venturi and the bowl. The carburetion and therefore the performance are thus degraded.